1. Field of the invention
The present invention concerns a method of vacuum packaging paste or liquid products in dispensers. The products concerned are usually cosmetic products or medicines which must be protected from contact with air because of the risk of oxidation or contamination. The dispenser usually comprises a variable volume reservoir (a deformable bottle, a tube closed by a piston, etc) closed in a sealed way by a dispensing valve which prevents ingress of air. The valve is advantageously associated with a precompression pump to guarantee clean dispensing and an acceptable rate of product feed. A device for implementing this method is also part of the invention, as are the resulting dispensers.
2. Description of the prior art
One prior art vacuum packaging method is disclosed in the U.S. Pat. No. 4,845,927 to RAPPARINI with the priority date of Jan. 21, 1987. It consists in first filling a small sac with the product to be packaged through an open side of the sachet. The filled sachet is then placed in a bucket so that the open side of the sac is at the top of the bucket. A bell is then lowered to hermetically seal the top of the bucket. The sachet is therefore enclosed in an enclosure from which the air is evacuated by a system of vacuum pumps. The patent then discloses that jaws are used to hot seal the open side of the small sac. It is only after this welding operation that the enclosure is returned to atmospheric pressure and the sachet is removed from the bucket by raising the bell.
In June 1988 the company VALOIS adapted this method to flexible tubes containing toothpaste. They used the idea of enclosing the tube in an enclosure adapted to be evacuated and inside which the bottom of the tube was then sealed before returning the enclosure to atmospheric pressure. The same company disclosed in French patent application No 89-14260 filed Oct. 31, 1989 a comparable method for attaching a dispensing valve to a bottle. Once vacuum was established in the enclosure, the valve was crimped to the bottle, for example, inside the enclosure and using clamps disposed for this purpose in the bell of the enclosure.
Although the use of a vacuum enclosure for sealing the packaging is particularly effective in the case of vacuum packaging a paste or liquid product, it does not enable all of the air to be eliminated from the dispenser finally obtained. If any air is trapped within the product itself, vacuum is not established in the enclosure, i.e. at the surface of the product contained in the reservoir of the dispenser which is still open at this time makes it impossible to evacuate it. It is therefore better if no air is included in the product in the dispenser. For this the reservoir must be filled with sufficient care.
The problem of trapping air bubbles arises in a particularly acute manner in the case of a tube with a piston such as that shown in axial cross-section in FIG. 1. This particular type of reservoir R comprises a cylindrical tube 10 whose bottom 13 is open. A cover 16 held by a sleeve 12 adapted to be force-fitted around the lower perimeter 14 of the tube 10 can be provided to protect the open bottom 13 from inadvertent pressure by the user and from soiling. Behind the cover 16, which has a vent hole 17, is a piston 50 adapted to move along the tube 10. A double lip seal 51 at its perimeter provides a seal at the area of contact between the piston and the tube.
A preferred form of the piston 50 is shown in the appended FIGS. 1 through 3. On its outside it comprises a ring 52 which projects sufficiently to abut against the cover 16 when the piston 50 is in the lowermost position (associated with the maximum content of the tube 10). Another ring 53 is provided on its inside. Its diameter, greater than that of the previous ring 52, is such that a dispensing valve V crimped to the neck 15 of the tube 10 is able to fit inside the ring 53 when the piston 50 reaches its uppermost position (associated with the minimum content of the tube 10). At this time the ring 53 abuts against the base of the neck 15.
The product can be fed into a tube 10 of this kind in two different ways using known filling techniques carried out at atmospheric pressure. The first (not shown) has the piston 50 remain at its lowermost position throughout the operation. An injector tube is then lowered through the open neck 15 of the tube 10 into the immediate vicinity of the piston 50. It delivers the product and is raised relative to the tube 10 as the quantity of product injected increases. Care is taken to keep the end of the injector tube above the surface of the product. This minimizes the risk of air bubbles becoming trapped in the product already introduced. However, the inclusion of small volumes of air is inevitable in practise. The presence of the ring 53 favors the occurrence of this unwanted phenomenon.
A second filling method already mentioned consists in starting with the piston 50 at the uppermost position (see FIG. 2). An injector tube 200 is inserted through the neck 15 of the tube 10 as in the first method. However, its end 201 is simply placed within the ring 53 of the piston 50. It is attached to a plug 210 which seals the neck 15 and so is isolated from the external environment. As schematically represented in FIG. 3, product 80 is then injected with sufficient pressure to push down the piston 50 as further quantities of product are introduced. On completion of filling by this method the volume of air initially contained between the piston 50 and the plug 210, that is to say in the neck 15, to all intents and purposes, remains trapped, the injection pressure causing it to be mixed with the product to form an emulsion 81.
An object of the present invention is to propose a method of vacuum packaging paste or liquid products in which the filling of the dispenser reservoir avoids any trapping of air bubbles. It must be particularly effective when the reservoirs are tubes closed by pistons like those just described.
This object is achieved by a new use of the enclosure previously used in the prior art for sealing dispensers in vacuum.